Pelleting of carbon black

ABSTRACT

Carbon black is formed into pellets by introducing carbon black and a pelletizing fluid into a pellet mill which contains a mixing device. The mixing device is driven by a motor which is connected to the device by a variable speed transmission. The flow of pelletizing fluid into the mill is controlled in response to a measurement of the power consumed by the motor. A measurement is made of the density of carbon black pellets removed from the mill. In response to this density measurement, the variable speed transmission is controlled so that pellets of uniform density are produced.

1 1 June 24, 1975 1 1 PELLETING OF CARBON BLACK Wilson 11. Rushiord,London. England [75] Inventor:

[73] Assignee: Phillips Petroleum Company,

Bartlesville. Okla.

[22] Filed: Mar. 13, 1974 [2]] Appl. No.: 450,576

[52] US. Cl. 425/140; 425/222; 23/314; 259/3; 264/117 [51] Int. Cl.8013' 2/12; CO9C 1/58 158] Field of Search H 23/314, 313; 425/222, 140;259/3, 85; 264/117 I 56] References Cited UNITED STATES PATENTS2.699.381 1/1965 King 23/314 2.800.399 7/1957 King 23/314 POWER SOURCEPOWER MEASUREMENT 3,266,873 8/1966 Alleman 23/314 3.266.874 8/1966Allcman 23/314 3,293.003 12/1966 .Iones 23/314 FOREIGN PATENTS ORAPPLICATIONS 698,539 11/1964 Canada 23/314 845.041 8/1960 United Kingdom23/314 952.220 3/1964 United Kingdom 23/314 Primary Examiner-NormanYudkoff Assistant Examiner-S. .1. Emery [57] ABSTRACT Carbon black isformed into pellets by introducing carbon black and a pelletizing fluidinto a pellet mill which contains a mixing device. The mixing device isdriven by a motor which is connected to the device by a variable speedtransmission. The flow of pelletizing fluid into the mill is controlledin response to a measurement of the power consumed by the motor. Ameasurement is made of the density of carbon black pellets removed fromthe mill. In response to this density measurement, the variable speedtransmission is controlled so that pellets of uniform density areproduced.

3 Claims, 1 Drawing Figure LK /PELLE'I'IZING FLUID PELLET MILL VARIABLESPEED TRANSM l SSlON PELLETING OF CARBON BLACK Loose carbon black asproduced has a very low density which makes it extremely difficult tohandle and transport. For this reason, it is common practice in theindustry to form the black into pellets which have a greater densitythan the loose black. This can be accomplished by the use of a pelletmill which contains a mixing device, such as a rotatable shaft having aplurality of pins extending therefrom. The loose black and an aqueouspelletizing liquid are introduced into the inlet of the mill, andpellets are withdrawn from the outlet of the mill. It is desirable thatthe pellets have a uniform bulk density in order to facilitate blendingof the carbon black into rubber or other products.

In view of the fact that loose carbon black is inherently difficult tohandle and process. it is often difficult to control pelletingoperations to produce the desired uniform pellets. One control procedurewhich has been employed heretofore involves measuring the power consumedby the driving means connected to the mixing device. ln response to thismeasurement, the flow of pelletizing liquid into the mill is regulatedso that substantially a constant amount of energy is imparted to themixing device. While this procedure greatly improves pelletingoperations. the bulk density of the produced pellets often is notcompletely uniform.

ln accorrdance with this invention, a carbon black pelleting operationis improved by measuring the bulk density of the pellets withdrawn fromthe pellet mill. In response to this measurement, the speed at which themixing device is operated in the pellet mill is varied to providepellets having a more uniform density.

The accompanying drawing is a schematic representation of carbon blackpelleting apparatus having an embodiment of the control system of thisinvention incorporated therein.

Referring now to the drawing in detail, there is shown a conventionalpellet mill 10 which comprises an elongated, generally cylindricalchamber having a mixing device positioned therein. This device cancomprise a rotatable shaft 11 having a plurality of spaced pins 12extending therefrom. Loose carbon black is passed from a storage vessel13 through a conduit 14 to the inlet end of pellet mill 10. A controlvalve, such as a rotatable star valve 15, is disposed in conduit 14 sothat the carbon black can be introduced at a relatively uniform rate. Apelletizing fluid. which normally comprises an aqueous liquid such aswater or a mixture of water and molasses, is introduced into the inletend of pellet mill through a conduit 16. The flow of fluid throughconduit [6 is regulated by a flow controller 17 which adjusts a valve18. Pellets are withdrawn from the outlet end of mill through a conduit20 which communicates with the inlet ofa dryer 21. Dried pellets areremoved through a conduit 22. The apparatus thus far describedconstitutes conventional carbon black pelleting and drying apparatus.

Shaft 11 of the mixing device is rotated by a motor 23 which isconnected to a power source 24. The drive shaft of motor 23 is connectedby a variable speed transmission 25 to shaft ll. Motor 23 is operated ata substantially constant speed. A power measuring element 26 measuresthe energy consumed by motor 23 and establishes an output control signalresponsive thereto. This device can be connected by transformer 27 toone of the power leads to the motor to measure the current through thislead, for example. The output signal from element 26 is applied as thesetpoint signal to flow controller 17. In this manner, the flow ofpelletizing fluid is adjusted in response to variations of powerconsumed by the motor, which in turn are representative of variations inenergy imparted to the mixing device in the pellet mill. The control ofthe flow of pelletizing fluid in this manner is known in the art, and isdescribed in U.S. Pat. No. 3,249,263, for example.

While the foregoing control system improves the uniformity of thepellets produced, it is desirable to provide an even greater control ofthe bulk density of the pellets. This is accomplished in accordance withthe present invention in response to a measurement of the bulk densityof the produced pellets. To this end, a conduit 30 extends betweenconduit 20 and a density measuring device 31 to supply a sample of theproduced pellets to the density measuring device. These pellets can bereturned to conduit 20 through a conduit 32. Density measuring device 31can be any one of the density measuring devices described in U.S. Pat.No. 3,807,523, for example. A tachometer 33 is connected to shaft 11 toestablish a signal representative of the speed of rotation of the shaft.This signal is applied to the input of a conventional controller 34which regulates variable speed transmission 25. The setpoint ofcontroller 34 is adjusted by the output signal from density measuringand control device 31. In the absence of a change in the output signalfrom device 31, transducer 33 operates through controller 34 andtransmission 25 to maintain a constant speed of rotation of shaft 11. Ifthe measured bulk pellet density should change, the setpoint ofcontroller 34 is adjusted so that the speed of rotation of shaft 11 ischanged. It has been found that the bulk density of the produced carbonblack pellets is increased when the speed of rotation of the mixingdevice is increased. In accordance with the invention, the speed isadjusted by variable speed transmission 25 so that pellets having apredetermined desired value of bulk density are produced. This requiresthe speed to be increased if the measured bulk density falls below adesired preselected value and decreased if the measured bulk densityrises above such value. Variable speed transmission 25 can be a deviceof the type described in Marks Mechanical Engineers Handbook,"McGraw-Hill Book Company, Inc., New York, I958, pages 10-52, forexample.

This density control of the pellet mill is particularly effective whenemployed in combination with control of the rate of introduction of thepelletizing fluid in response to a measurement of the energy imparted tothe mixing device. The two control elements operating together functionto produce pellets of uniform bulk density.

As an example of a typical operation of the control method of thisinvention, pellet mill 10 can have a diameter of about 20 inches and alength of about 9 feet. Shaft 11 is rotated at a speed of about 320revolutions per minute in normal operation. Carbon black, such as typeN330, is introduced into mill 10 at a rate of about 1,750 pounds perhour. The pelletizing liquid is water containing about 0.5 to 1.0 weightpercent molasses. This liquid is normally introduced into mill 10 at arate of about 1,750 pounds per hour. The bulk density of loosely packedpellets produced in mill 10 is maintained at about 22 pounds per cubicfoot. The calibration of controller 34 can readily be adjusted in agiven operation from a measurement of the change in density whichresults from a given change in speed of shaft rotation. The controlapparatus is then set to produce carbon black having a desired bulkdensity.

While this invention has been described in conjunction with a presentlypreferred embodiment, it should be evident that it is not limitedthereto.

What is claimed is: 1. Apparatus for pelleting carbon black comprising:a generally horizontal pellet mill having a carbon black inlet, a pelletoutlet, and axial rotary pin agitator mixing means positioned with saidpellet mill;

conduit means communicating with said pellet mill to introduce apelletizing liquid;

a motor;

a variable speed drive means connected said motor to said mixing means;

means to measure the bulk density of a volume of pellets removed fromthe outlet of said pellet mill and to establish a signal representativeof the measured bulk density; and

means responsive to said signal to control said variable speed drivemeans to adjust the speed at which said mixing means is rotated inresponse to changes in the measured density said responsive meansaetuating said mixing means at a lower rate of speed if the measuredbulk density increases above a predetermined value and at a higher rateof speed if the measured bulk density decreases below said predeterminedvalue.

2. The apparatus of claim 1. further comprising means to measure thepower consumed by said motor and to establish a second signalrepresentative thereof, and means responsive to said second signal tocontrol the flow of pclletizing fluid through said conduit means.

3. The apparatus of claim 2 wherein said motor is an electric motorwhich operates at substantially a constant speed, and wherein said meansto measure power consumed comprises means to establish a signalrepresentative of current supplied to the motor.

UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OF CORRECTIONPATENT NO. 3,891,366

DATED 1 June 24, 1975 |NVENTOR(S) 3 Wilson H. Rushford It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, line 21, delete "3,807,523" and insert therefor Signed andScaled this A ttesr:

RUTH C. MASON C. MARSHALL DANN Arresting Officer Commissioner ufParenlsand Trademarks UNITED STATES PATENT AND TRADEMARK OFFICE CERTIFICATE OFCORRECTION PATENT NO. 3,891,366

DATED 1 Jun 2TH 1975 INVENTOR(S) 1 Wilson H. Rushford tt is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 3, line 11, delete "with" and insert therefor within column 3,line 15, delete "connected" and insert therefor connecting [SEAL]Arrest:

RUTH C. MASON Arresting Officer Signed and Scaled this seventeenth D 3yOf February 1976 C. MARSHALL DANN Commissioner uj'larerrls andTradvnwrks

1. APPARATUS FOR PELLETING CARBON BLACK COMPRISING: A GENERALLYHORIZONTAL PELLET MILL HAVING A CARBON BLACK INLET, A PELLET OUTLET, ANDAXIAL ROTARY PIN AGITATOR MIXING MEANS POSITIONED WITH SAID PELLET MILL;CONDUIT MEANS COMMUNICATING WITH SAID PELLET MILL TO INTRODUCE APELLETIZING LIQUID; A MOTOR; A VARIABLE SPEED DRIVE MEANS CONNECTED SAIDMOTOR TO SAID MIXING MEANS; MEANS TO MEASURE THE BULK DENSITY OF AVOLUME OF PELLETS REMOVED FROM THE OUTLET OF SAID PELLET MILL AND TOESTABLISH A SIGNAL REPRESENTATIVE OF THE MEASURED BULK DENSITY; AND 2.The apparatus of claim 1, further comprising means to measure the powerconsumed by said motor and to establish a second signal representativethereof, and means responsive to said second signal to control the flowof pelletizing fluid through said conduit means.
 3. The apparatus ofclaim 2 wherein said motor is an electric motor which operates atsubstantially a constant speed, and wherein said means to measure powerconsumed comprises means to establish a signal representative of currentsupplied to the motor.